1. Field of the Invention
The present invention relates to a multilayer capacitor.
2. Description of Related Art
Multilayer capacitors are one example of multilayer electronic components and are widely used as electronic components having small sizes, high capacity and high reliability. Electric and electronic devices have a large number of multilayer capacitors used therein. As devices have been becoming smaller in size and achieving higher performance in recent years, further improvement of multilayer capacitors in terms of small size, high capacity, low cost and high reliability is even more strongly demanded.
Ferroelectric ceramic material is typically used for currently available small-size and high-capacity multilayer capacitors. When an electric field is applied to such ferroelectric ceramic material, mechanical distortion, namely, electrostriction, occurs in the material. Accordingly, when electric voltage is applied to a multilayer capacitor made of ferroelectric ceramic material, the capacitor vibrates due to electrostriction.
In the case where a multilayer capacitor is mounted onto a circuit board, such electrostrictive vibration of the multilayer capacitor may be transmitted to the board, and not only the multilayer capacitor itself but the board and the peripheral components may vibrate, which may emit vibration sounds of audible frequency (20-20,000 Hz). Some vibration sounds are in a frequency range which is uncomfortable for humans, and solutions for such vibration sounds are demanded.
In order to prevent the multilayer capacitor vibration due to electrostriction from being transmitted to the board, Japanese Unexamined Patent Publication No, 2004-335963 (Patent Document 1) proposes providing the multilayer capacitor with electrode connection parts for connecting external terminal electrodes to the board to make a certain separation between the board and the undersurface of the capacitor's main body.
However, when adopting the method of making a certain separation between the board and the capacitor's main body using the electrode connection parts, such addition of the electrode connection parts may increase the manufacturing cost or complicate the manufacturing processes, so further improvement is required.
Meanwhile, in Japanese Unexamined Patent Publication No. 2007-258476 (Patent Document 2), the dielectric layer that constitutes a multilayer capacitor is formed of a dielectric ceramic composition that contains, as major components thereof, BaTiO3, SrTiO3 and CaTiO3, wherein these components do not substantially form a solid solution but instead form a composite structure. In Patent Document 2, an electrode paste film, which will be an internal electrode layer after being fired, is formed with electrode paste that includes conductive powder and a common material containing BaTiO3 powder, SrTiO3 powder and CaTiO3 powder wherein the content of the BaTiO3 powder is in a specific range.
In contrast to the material approach used in Patent Document 2, Japanese Unexamined Patent Publication No. 2011-018758 (Patent Document 3) proposes a solution through a structural approach. Specifically, Patent Document 3 discloses that a first internal electrode electrically connected to a first terminal electrode, a second internal electrode electrically connected to a second terminal electrode and a third internal electrode electrically isolated from the first and second terminal electrodes are disposed such that a dielectric layer is sandwiched by the first and third internal electrodes and also sandwiched by the second and third internal electrodes, thereby achieving a configuration of two capacitive components being serially connected. In this configuration, the third internal electrode has a narrow-width portion in an area where no capacitive component is formed, the narrow-width portion having a width smaller than that of an active portion in which the third internal electrode faces the first internal electrode and the second internal electrode. An opening is formed with this narrow-width portion so that the portion where no electrode is formed in the center thereof has a larger area, and as a result, the dielectric layers can be fixed with strong adhesion to each other when the element body is fired.    Patent Document 1: Japanese Unexamined Patent Publication No. 2004-335963    Patent Document 2: Japanese Unexamined Patent Publication No. 2007-258476    Patent Document 3: Japanese Unexamined Patent Publication No. 2011-018758